Inkjet printing involves depositing droplets of liquid ink onto a printing medium from one or more printer heads. The printer heads are coupled with a container containing ink. Ink is ejected from one or more nozzles of the print heads when a piezoelectric crystal in the print head is actuated. The piezoelectric crystal generates a pulse in the ink so that the ink expels through the nozzle as a droplet. To create the image, a carriage which holds one or more print heads scans or traverses across the printing medium, while the print heads deposit ink as the printing medium moves.
Large format printing is performed to create signs, banners, museum displays, sails, bus boards, POP applications, and the like. Oftentimes consumers of large format prints prefer to choose a full or partial gloss finish to create striking displays. Gloss finishes come in various reflective intensities measured in Gloss Number. Gloss Number measures how much light is reflected at a given position. In today's art, gloss finishes are commonplace with solvent based SWF printers, but a high gloss finish is not available on today's UV printers due to the fact that the curing of the droplets of UV ink leaves a matte surface structure, rather than a very smooth finish.
Spot gloss allows one to put gloss coating on some parts of a printed image while leaving other parts uncoated. For instance, one may want to apply gloss coating to a company logo, and leave the rest of the image in a matte finish. If spot gloss is needed in inkjet printing, the background image normally is printed first, and then the printing media is reversed back through the printer carriage for a second run, or the media is removed and reloaded. This approach requires additional handling of the media, which decreases throughput and which can also result in registration errors. Alternatively, a multilayer technique can be used to print a layer of clear inks on a target area to create a spot gloss or a gloss overcoat. In this approach, a clear ink channel is required to achieve the spot gloss and/or a gloss overcoat.